How to get Pandas column multiindex names as a list

Question

I have the following CSV data:

id,gene,celltype,stem,stem,stem,bcell,bcell,tcell id,gene,organs,bm,bm,fl,pt,pt,bm 134,foo,about_foo,20,10,11,23,22,79 222,bar,about_bar,17,13,55,12,13,88 

And I can successfully summarize them this way:

import pandas as pd df = pd.read_csv("http://dpaste.com/1X74TNP.txt",header=None,index_col=[1,2]).iloc[:, 1:]  df.columns = pd.MultiIndex.from_arrays(df.ix[:2].values) df = df.ix[2:].astype(int) df.index.names = ['cell', 'organ'] df = df.reset_index('organ', drop=True)  result = df.groupby(level=[0, 1], axis=1).mean() result = result.stack().replace(np.nan, 0).unstack() result = result.swaplevel(0,1, axis=1).sort_index(axis=1) 

Which looks like:

In [341]: result Out[341]:         bm               fl               pt      bcell stem tcell bcell stem tcell bcell stem tcell cell foo      0   15    79     0   11     0  22.5    0     0 bar      0   15    88     0   55     0  12.5    0     0 

My question is, from result how can I get the column index of the first level as list:

['bm','fl','pt'] 

Answer 1

result.columns returns a pandas.core.index.MultiIndex which has a levels attribute.

list(result.columns.levels[0]) 

returns

['bm', 'fl', 'pt'] 

Answer 2

Additionally you could use columnns.get_level_values(level)

 >>> result.columns.get_level_values(0).unique()     array(['bm', 'fl', 'pt'], dtype=object)  >>> list(result.columns.get_level_values(0))     ['bm', 'bm', 'bm', 'fl', 'fl', 'fl', 'pt', 'pt', 'pt']